The theme of sleep purports to be the book’s unifying thread, to the point that the novel is divided into parts corresponding to the various stages of sleep.
In reality, it is a device—perhaps overly intellectual—to tell the story of the love between Robert and Sarah.
We find ourselves in a university hall of residence.
Sarah suffers from a sleep disorder that leads her to confuse dreams with reality.
At their first meeting, Robert tells her he has just lost a cat to which he was deeply attached.
Sarah dreams that Robert has lost a twin sister, Cleo, who does not actually exist.
And it is upon this misunderstanding, originating in Sarah’s secret—her sleep disorder—that their relationship takes root:

as she left, they looked directly into each other's eyes for the first time; and something happened then, some connection was made, just for a moment

.
Their relationship is built on confidences, which

ranged freely over feelings, friendship, families and gender, shared intimacies and self-revelations which became deeper and more frequent as the objects themselves grew larger and more complex

.
The relationship between Robert and Sarah cannot, however, develop into a true romantic affair, partly because Sarah is a lesbian and partly due to Robert’s inability to translate his feelings into romantic advances.
Their story remains in limbo until Sarah’s and Robert’s paths diverge: their university years come to an end, and when Sarah terminates a relationship with a woman, Robert realizes he is incapable of seizing this opportunity to translate his affection for his friend into a sexual relationship.
At this point, the plot (in truth, the narrative constantly jumps between past and present, complicating the reading experience) shifts into the future, when the university residence has been converted into a sleep clinic—as it turns out, run by Sarah’s first lover, a paranoid man convinced that his mission in life is to find a way not to sleep.
This is the least convincing section of the book, which seems to slide into a thriller, peppered with superficial musings on psychological science and references to analogies between dreams, fantasy, and cinema.
The finest pages are those chronicling the life of Sarah, now a schoolteacher, in some way haunted by her sleep disorder—with which she has come to terms—and ever waiting for Robert, the only person with whom she knows she is truly in tune.
Only towards the end of the novel is it revealed that Robert has undergone gender reassignment (because he understood his true nature, or out of love for Sarah?), becoming Cleo, a physician specializing in sleep disorders.
And, like any thriller, everything is resolved, and Cleo can finally reveal herself to Sarah.

The book’s primary virtue is the prose: pleasant, brilliant, and fluid.
Its chief flaw is the inconclusiveness of the events and the characters: everything remains superficial, creating a palpable disconnect between the narrative structure of a thriller and the unmistakable ambition to deliver something more.
What, exactly? It is impossible to say.

Why read it? The individual pages read exceptionally well; the story as a whole disappoints.

The house of sleep